The present invention relates to a device for gluing the tail edge of web material wound in roll form, for example a roll of paper, toilet paper, all-purpose drying paper and the like. The invention also relates to a method for gluing the tail edge of rolls of wound web material.
In the paper converting industry, for example for the production of rolls of toilet paper, all-purpose drying paper, printing paper and the like, rolls or so-called xe2x80x9clogsxe2x80x9d of web material are frequently produced from large-diameter reels supplied from the paper mill. The rolls or logs are formed in rewinding machines and are then unloaded toward a gluing device which applies glue between the tail edge of the web material and the surface of the roll so as to cause the tail edge to adhere to said roll. The roll is then conveyed towards other processing stations, in particular towards a cutting machine which cuts the roll into small rolls of smaller length, destined for packaging and for sale.
U.S. Pat. No. 5,681,421 describes a gluing device comprising a roll feed path which has, along it, a station in which positioning of the free tail edge of the web material is performed so as to be able to perform subsequent gluing. In the positioning station the log is brought into contact with two movable members consisting, for example, of a roller and a belt. By controlling the movement of these members, the roll is temporarily stopped in the positioning station and the tail edge of the web material is sucked into a cavity or recess located underneath the roll feed path. Downstream of the positioning station there is a dispenser which, in one of the embodiments described, has a movable element which removes glue from a tank and conveys it up to a height of a surface for rolling of the roll, in correspondence of a slit.
By controlling the speed of the movable members making contact with the roll in the positioning station, said roll is fed towards the glue dispensing slit and, rolling over it, receives the glue on a portion of the roll surface, for example along a generatrix. By continuing the rolling movement, the tail edge is made to adhere to the surface of the roll where the glue has been applied.
EP-A-0742169 describes a substantially identical gluing method in which the positioning station is provided with two rollers located at a distance from each other and forming the movable members making contact with the roll. The movement of these two rollers is controlled so as to perform correct positioning of the free tail edge and the subsequent unloading of the roll onto an inclined surface where it receives the glue in the manner described above.
In these known devices and methods the glue is applied onto the external surface of the roll after raising and partially unwinding the tail edge.
In certain cases, however, the glue must be applied onto the tail edge instead of onto the material which is still wound. This requirement may arise depending on the type of material to be glued and, in particular, when the web material consists of a twin ply of very absorbent paper. When applying glue onto the surface of the roll insufficient gluing of the tail edge may occur since only the innermost ply of the tail edge adheres to the roll surface. In addition to this, an excessive amount of glue may be absorbed by the inner wound turns of web material. In other cases, if the material is not very absorbent and has two (or more) plies, it may be necessary to apply the glue with a certain pressure in order to cause it to seep through to the second ply, i.e. the outermost ply.
JP-5035562 describes a gluing device and method in which the roll to be glued is positioned on a pair of rotating rollers defining a cradle on which the roll is retained and made to rotate by rotation of the two rollers. The two rollers have, arranged underneath them, a glue dispenser which, in one of the embodiments described, is in the form of a movable bar which conveys the glue upwards from an underlying reservoir. The bar is brought into contact with the roll resting on the two rollers, after stopping rotation of the roll in a suitable angular position with the tail edge arranged between the two rollers. When gluing has been completed, the roll is wound up and expelled from the cradle formed by the two rollers, by means of a thruster.
In this known device gluing is also performed by necessarily applying the glue onto the roll surface instead of onto the tail edge. Moreover, in this device the gluing times are particularly long.
When the rolls to be glued have a large diameter, in devices where sealing of the tail edge is performed by means of rolling there may be the drawback that an excessively long rolling path is required in order to obtain winding-up of the tail edge and application of a gluing pressure onto the zone which has received the glue.
A first object of the present invention is to provide a device and a method for gluing, i.e. sealing, the tail edge of rolls of web material, by means of which even large-diameter rolls may be easily glued.
In particular, within the scope of this general object, the invention aims to provide a device and a method in which it is possible to glue the tail edge of large-diameter rolls without the need for lengthening excessively the roll feed path.
Moreover, an object of the invention is to provide a device and a method which may be adapted in an easy and efficient manner, also in terms of production speed, for the processing also of rolls having a greatly variable diameter.
According to another aspect of the present invention, the object of the invention is to provide a method and a device which allow rapid and reliable gluing also in the case where the glue must be applied onto the tail edge instead of onto the roll surface, while maintaining the possibility of performing gluing by means of application of the glue onto the roll surface, should this be required.
The object of an improved embodiment of the invention is to provide a device which allows gluing of the rolls by applying the glue either onto the external surface of the roll or onto the internal surface of the tail edge of the web material.
These and further objects and advantages, which will become clear to persons skilled in the art from a reading of the text which follows, are obtained by means of an improvement to the gluing device of the type comprising: a path for feeding of the roll to be glued; a station for unwinding and positioning the tail edge along the feed path; in the unwinding and positioning station, a first movable member and a second movable member which make contact with the roll during positioning of the tail edge and which define the position in which unwinding and positioning of the edge is performed; a glue dispenser with a reservoir and a dispensing element movable along a dispensing path, which is immersed in the glue and emerges from the glue so as to apply glue onto the web material.
According to a first aspect of the invention in a device of this type it is envisaged that the dispensing path along which the movable dispensing element moves, as well as the first and the second movable members in the positioning station, are arranged so that the dispensing path intersects the surface of the roll when the latter is in the condition where it is positioned in contact with the first and the second movable members of the positioning and unwinding station.
As will emerge clearly from the detailed description below of an example of embodiment, as a result of this arrangement, it is possible to dispense the glue (by means of the movable dispensing element) onto the surface of the roll, retaining the latter between the first and the second movable members, and then expel the roll from the positioning and unwinding station, causing it to pass between the two movable members. Sealing of the tail edge may be achieved in this case either by means of rolling along a rolling path downstream of the positioning station or by temporarily keeping the roll in the positioning station in contact with the two movable members, the movement of the latter causing the roll to rotate about its axis.
In order to obtain suitable positioning of the roll so as to simplify the path which must be followed by the movable dispensing element, the first and the second movable members of the positioning and unwinding station will be preferably arranged close to each other. Consequently, in order to allow subsequent feeding of the roll and unloading thereof from the positioning station, the first and the second members of the positioning station are movable relative to one other so as to move away from each other cyclically whenever a roll passes through.
The first and/or the second movable member may be preferably constructed as motorized rollers, even though it is possible for one or both of them to be constructed differently, for example in the form of continuous flexible members such as belts or the like.
In order to allow the movement away from each other of the first and the second movable members, the second of said members may be mounted on an oscillating arm advantageously equipped with a weight balancing means, for example a spring, in particular an air spring or the like.
The dispensing path followed by the movable dispensing element is preferably at least partly a rectilinear path. It is preferably inclined with respect to the vertical and oriented towards the station for positioning of the tail edge.
According to a particularly advantageous embodiment of the invention, the roll feed path, downstream of the first movable member of the positioning station, is provided (in a manner known per se) with a suction recess arranged underneath the feed path and having an axis mouth inside which the tail edge of the web material is sucked. In this case means may be provided for arranging, in the vicinity of the access mouth of the suction recess, a section bar for supporting the tail edge of the roll. This section bar extends so as to intersect the dispensing path of the movable dispensing element. In this way, when it is required to apply the glue onto the internal surface of the free edge instead of onto the external surface of the roll, the supporting section bar may be arranged in its operating position so that the free edge rests on It. The movement of the movable dispensing element in this case applies the glue onto the internal surface of the tail edge. xe2x80x9cInternal surfacexe2x80x9d is understood as meaning that surface which, during winding-up, adheres onto the surface of the roll.
Where the device is provided with a suction recess, the first movable member of the positioning station will be advantageously arranged upstream of the suction recess with respect to the direction of feeding of the rolls, whereas the second movable member will extend preferably downstream of the suction recess. Where the second movable member consists of a roller, it will preferably be located downstream of the suction recess. If the second movable member consists of a continuous belt, it may be arranged entirely downstream of the suction recess or partially upstream and partially downstream thereof.
The suction recess may comprise two suction systems which are independent from one another and respectively arranged on the bottom of the recess and on a side wall thereof so as to facilitate the operations of positioning and retention of the tail edge during application of the glue, preventing the vacuum which is produced from sucking in the glue.
According to another aspect, the invention also relates to a device for gluing the tail edge of a roll of wound web material, comprising: a feed path for said roll; along said path a station for unwinding and positioning the tail edge of the roll; in said unwinding and positioning station, movable members making contact with said roll so as to unwind and position the free edge; a glue dispenser comprising a glue reservoir and a dispensing element which is movable along a dispensing path and which is immersed in said glue and, moving upwards, dispenses glue for gluing of the tail edge. In a characteristic manner the device comprises a support section bar on which the tail edge of the roll rests, said dispensing path intercepting said section bar so as to apply the glue onto the surface of the tail edge which, by means of subsequent winding-up, comes into contact with the roll surface. It is thus possible to glue rolls which require the application of a glue on the internal surface of the free edge. In particular, it is advantageously envisaged that the section bar may be removable so that said device may be also used for gluing rolls where the glue may be applied onto the external surface of the roll instead of onto the free edge. According to this further aspect of the invention, the dispensing element need not follow a path which intersects the surface of the roll which is located in the unwinding and positioning station, although this is advantageous and preferable, so as to provide a machine which is able to glue rolls using three different operating methods, as will emerge clearly from the description below.
Further advantageous features of the gluing device and methods according to the invention are described in the accompanying claims.